1. Field of the Invention
The present invention generally relates to a capacitor, and more particularly, to a capacitor having a cathode spaced from an anode. The cathode is of an active material supported on a casing sidewall or a conductive substrate in contact with the casing sidewall. The anode is typically in the form of a sintered valve metal pellet, such as a sintered tantalum pellet that has been anodized and subjected to a formation step. The anode and cathode are kept from direct physical contact with each other by a separator that covers the cathode with a margin of the separator secured to the casing sidewall adjacent to the cathode material.
Conventional designs have the anode contained in a separator that surrounds and envelopes the anode pellet.
2. Prior Art
FIGS. 1 and 2 are side and top cross-sectional views respectively of a flat electrolytic capacitor 10 according to the prior art. The prior art capacitor 10 comprises an anode 12 and a cathode 14 housed inside a hermetically sealed casing 16. The capacitor electrodes are contacted with a working electrolyte (not shown) contained inside casing 16. Casing 16 includes a deep drawn can 18 having a generally rectangular shape comprised of spaced apart sidewalls 20 and 22 meeting with opposed end walls 24 and 26, the sidewalls 20, 22 and end walls 24, 26 extending upwardly from a bottom wall 28. A lid 30 is secured to sidewalls 20 and 22 and end walls 24 and 26 by a weld 32 to complete the casing 16. Casing 16 is made of a conductive metal and serves as one terminal or contact for making electrical connection between the capacitor and its load.
Anode 12 is in the form of a sintered pellet of a material selected from the group consisting of tantalum, aluminum, titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium, silicon, germanium, and mixtures thereof. As well known to those skilled in the art, after sintering, the anode pellet is anodized.
Cathode 14 is spaced from the anode 12 and comprises conductive substrates 34 supporting a cathode active material 36. In FIGS. 1 and 2, the conductive substrates 34 are the casing sidewalls 20, 22. While not shown in the drawings, the conductive substrates 34 can alternatively be a separate conductive member that is contacted to the inner surface of the casing sidewalls 20, 22. Ruthenium oxide is one of a number of suitable cathode active materials.
A separator structure includes spaced apart sheets 38 and 40 of insulative material, for example a microporous polyolefinic film. The separator sheets 38 and 40 are connected to a polymeric ring 42 and disposed intermediate anode 12 and the coated sidewalls 20, 22 serving as the cathode.
Alternatively, the polymer ring 42 is eliminated and the separator sheets 38, 40 are secured to each other adjacent to their edges.
The other electrical terminal or contact is provided by a conductor or lead 44 extending from the anode 12 and through lid 30. Lead 44 is electrically insulated from lid 30 by an insulator and seal structure 46. The anode 12 is provided with a notch forming a step 48 adjacent to end wall 26 of can 18. Step 48 provides clearance for the insulator and seal structure 46. In that manner, the portion of anode terminal lead 44 extending outside the capacitor 10 for connection to the load is hermetically sealed from the interior of the capacitor 10 and electrically insulated from the can 18 and lid 30 serving as the terminal for the cathode 14.
An electrolyte fill opening is provided for filling an electrolyte (not shown) into the capacitor, after which this opening is sealed with closure member 50 that is preferably welded in place.
While positioning the anode in a separator envelope to prevent the opposite polarity electrodes from contacting each other is acceptable, there is a desire to improve manufacturability of capacitors, for example electrolytic capacitors. Improved manufacturability is realized by covering the cathode with a separator material instead of containing a sintered pellet-type valve metal anode in a separator envelope.